Recommendations for improving predictions of the long-term environmental behaviour of 14C, 36Cl, 99Tc, 237Np and 238U

R. Avila (Facilia), Y. Thiry (SCK-CEN), R. Gilbin (IRSN), A. Agüero (CIEMAT), M. Thorne (Mike Thorne and Associates Ltd), M. Sheppard (Ecomatters), C. Tamponnet (IRSN), A. Ikonen (Posiva OY) and S. Xu (SSI)

Rapport IUR n° 6, 2006, ISBN 978-0-9554994-2-5

The International Union of Radioecology (IUR) created a Task Force “Radioecology and Waste” with the overall objective of promoting cooperation between radioecologists for research in the field of radioactive waste management.
This report provides an overview of the available knowledge related to the behaviour of ¹⁴C, ³⁶Cl, ⁹⁹Tc, ²³⁷Np, ²³⁸U in both terrestrial and aquatic ecosystems based on information that has been collated by experts through the activities of this Task Force. The findings have been made available to the BIOPROTA group, and collaboration with BIOPROTA has been maintained through the work of the Task Force.
An overview of the behaviour of the studied radionuclides is presented with the help of interaction matrices that were developed for terrestrial and aquatic environments. These matrices identify the main components and processes that describe the behaviour of the radionuclides in these two broad environment types. Furthermore, the potentially relevant processes were identified for each specific studied radionuclide (¹⁴C, ³⁶Cl, ⁹⁹Tc, ²³⁷Np, ²³⁸U).
There are wide differences in data availability and process descriptions between the five studied radionuclides. For ¹⁴C there is a good understanding of the behaviour, supported by empirical data, as opposed to ²³⁷Np where there are few empirical data and assessments are usually done using data and knowledge from analogue elements, e.g. uranium and plutonium. New experimental studies should therefore be initiated to fill these gaps.
General approaches for improvement of the assessments models were also summarised, together with the needs for research and development for each specific radionuclide. Conclusions, recommendations and proposed future work by the Task Force are provided. For example, interaction matrices for other radionuclides (e.g. ⁵⁹Ni, ⁷⁹Se, ⁹⁴Nb, ¹²⁹I, ²²⁶Ra, ²³⁹Pu, and ²⁴¹Am) should be developed, supported by descriptions of the relevant processes and the identification of preferred ways of modelling.